I'm amazed that engineers can make submerged tunnels work and that leaks don't (literally) sink the whole plan.
ianburrell 4 hours ago [-]
The Transbay Tube carrying BART across the bay is immersed tube. The sections were welded together by divers. The sections were filled with water and then pumped out.
Fehmarnbelt tunnel sections are concrete. I couldn't find how they are connected by concrete would make sense.
imglorp 3 hours ago [-]
A video posted in another thread says the segments are sealed with bulkheads, floated into position, submerged by allowing water into a ballast section, dropped into place , aligned with pins, drawn to the next segment with hydraulic jacks, and sealed to it with rubber gaskets. Then the bulkheads can be removed. The gaskets also allow for some thermal expansion.
I'm curious what the lifetime of those gaskets might be and how you might maintain them.
SoftTalker 1 hours ago [-]
The "ballast sections" may act as bilges, so that any leaks will accumulate there and can be pumped out. 100% water-tightness is not essential. Occasional re-grouting/caulking of the joints may be good enough.
bobthepanda 3 hours ago [-]
I figure once you join them, you could also apply waterproofing to the outside as well, no?
lmm 3 hours ago [-]
Maybe. What would that look like, adding more gaskets on the outside? That sounds even harder to maintain since the only way to get access is diving.
euroderf 1 hours ago [-]
Some kind of goop that would get very slowly squeezed into gaps by water pressure ?
2 hours ago [-]
bloggie 49 minutes ago [-]
Here’s a fun video about how one sunken tunnel was built in Vancouver back in the 50s. https://youtu.be/A1igKk8eK0M
readthenotes1 4 hours ago [-]
52.6B krone for 18 km
8B USD for 11 miles
CACHSR IOS 36B USD for 171 miles.
The Merced to Bakersfield IOS looks like a bargain on a distance basis. I have no idea of the carbon offset or passenger time saving versus flying of course
bradchris 4 hours ago [-]
Well, if we’re comparing CA infra costs, for a more 1-1 comparison you can look at the $9.7B Los Angeles is spending on building out a long-awaited subway line (phase 1 of 3 opened Friday!) and see how tunneling underwater looks like a bargain in comparison.
Fehmarnbelt tunnel sections are concrete. I couldn't find how they are connected by concrete would make sense.
I'm curious what the lifetime of those gaskets might be and how you might maintain them.
8B USD for 11 miles
CACHSR IOS 36B USD for 171 miles.
The Merced to Bakersfield IOS looks like a bargain on a distance basis. I have no idea of the carbon offset or passenger time saving versus flying of course
https://www.latimes.com/california/story/2026-05-07/los-ange...